Just wanted to follow up that I've been using xylitol continuously since I started -- interesting to realize it's been 6 years now! I still just put a pinch of granules in my mouth after I brush, let it dissolve, swish and then spit it back out. Seems to be great. On the odd occasion when I don't use it (forgot to bring on an overnight trip for example), it feels very strange. I feel like my teeth don't get nearly as clean without it.
I haven't found it to affect my teeth color any. If anything, it may whiten them slightly. (However, my passion for green tea is counteracting that).